Meanwhile, there are clear opportunities for pickups in Alaska, Louisiana, Arkansas, Michigan, Montana, North Carolina, and New Hampshire. The only competitive states Republicans need to defend are the seats of Minority Leader Sen. Mitch McConnell in Kentucky and a Georgia seat to be vacated by the retiring Sen. Saxby Chambliss.

The new Washington Post/ABC poll showed that Democrats' perceived advantage on key issues is not carrying over to a structural advantage on the ballot. Voters trust Democrats more than Republicans on handling health care (44-36), immigration (44-36), energy policy (43-35), and helping the middle class 47-34).

But Obamacare remains deeply unpopular with the public. Only 38% approve of how Obama is implementing the federal health-care law, while 57% disapprove.